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USB(4) FreeBSD Kernel Interfaces Manual USB(4)
NAMEusb -- Universal Serial Bus
SYNOPSISdeviceusb#include <dev/usb/usb.h>
#include <dev/usb/usbhid.h>
DESCRIPTION
FreeBSD provides machine-independent bus support and drivers for USB
devices.
The usb driver has three layers: the controller, the bus, and the device
layer. The controller attaches to a physical bus (like pci(4)). The USB
bus attaches to the controller, and the root hub attaches to the con-
troller. Any devices attached to the bus will attach to the root hub or
another hub attached to the USB bus.
The uhub device will always be present as it is needed for the root hub.
INTRODUCTION TO USB
The USB is a 12 Mb/s serial bus (1.5 Mb/s for low speed devices). Each
USB has a host controller that is the master of the bus; all other
devices on the bus only speak when spoken to.
There can be up to 127 devices (apart from the host controller) on a bus,
each with its own address. The addresses are assigned dynamically by the
host when each device is attached to the bus.
Within each device there can be up to 16 endpoints. Each endpoint is
individually addressed and the addresses are static. Each of these end-
points will communicate in one of four different modes: control,
isochronous, bulk, or interrupt. A device always has at least one end-
point. This endpoint has address 0 and is a control endpoint and is used
to give commands to and extract basic data, such as descriptors, from the
device. Each endpoint, except the control endpoint, is unidirectional.
The endpoints in a device are grouped into interfaces. An interface is a
logical unit within a device; e.g. a compound device with both a keyboard
and a trackball would present one interface for each. An interface can
sometimes be set into different modes, called alternate settings, which
affects how it operates. Different alternate settings can have different
endpoints within it.
A device may operate in different configurations. Depending on the con-
figuration, the device may present different sets of endpoints and inter-
faces.
The bus enumeration of the USB bus proceeds in several steps:
1. Any device specific driver can attach to the device.
2. If none is found, any device class specific driver can attach.
3. If none is found, all configurations are iterated over. For each
configuration, all the interfaces are iterated over, and interface
drivers can attach. If any interface driver attached in a certain
configuration, the iteration over configurations is stopped.
4. If still no drivers have been found, the generic USB driver can
attach.
USB CONTROLLER INTERFACE
Use the following to get access to the USB specific structures and
defines.
The /dev/usbN can be opened and a few operations can be performed on it.
The poll(2) system call will say that I/O is possible on the controller
device when a USB device has been connected or disconnected to the bus.
The following ioctl(2) commands are supported on the controller device:
USB_DISCOVER
This command will cause a complete bus discovery to be initiated.
If any devices attached or detached from the bus they will be
processed during this command. This is the only way that new
devices are found on the bus.
USB_DEVICEINFO structusb_device_info
This command can be used to retrieve some information about a
device on the bus. The udi_addr field should be filled before
the call and the other fields will be filled by information about
the device on that address. Should no such device exist, an
error is reported.
#define USB_MAX_DEVNAMES 4
#define USB_MAX_DEVNAMELEN 16
struct usb_device_info {
u_int8_t udi_bus;
u_int8_t udi_addr; /* device address */
usb_event_cookie_t udi_cookie;
char udi_product[USB_MAX_STRING_LEN];
char udi_vendor[USB_MAX_STRING_LEN];
char udi_release[8];
u_int16_t udi_productNo;
u_int16_t udi_vendorNo;
u_int16_t udi_releaseNo;
u_int8_t udi_class;
u_int8_t udi_subclass;
u_int8_t udi_protocol;
u_int8_t udi_config;
u_int8_t udi_speed;
#define USB_SPEED_LOW 1
#define USB_SPEED_FULL 2
#define USB_SPEED_HIGH 3
int udi_power;/* power consumption in mA, 0 if selfpowered */
int udi_nports;
char udi_devnames[USB_MAX_DEVNAMES][USB_MAX_DEVNAMELEN];
u_int8_t udi_ports[16];/* hub only: addresses of devices on ports */
#define USB_PORT_ENABLED 0xff
#define USB_PORT_SUSPENDED 0xfe
#define USB_PORT_POWERED 0xfd
#define USB_PORT_DISABLED 0xfc
};
udi_bus and udi_addr contain the topological information for the
device. udi_devnames contains the device names of the connected
drivers. For example, the third USB Zip drive connected will be
umass2. The udi_product, udi_vendor and udi_release fields con-
tain self-explanatory descriptions of the device. udi_productNo,
udi_vendorNo, udi_releaseNo, udi_class, udi_subclass and
udi_protocol contain the corresponding values from the device
descriptors. The udi_config field shows the current configura-
tion of the device.
udi_peed indicates whether the device is at low speed
(USB_SPEED_LOW), full speed (USB_SPEED_FULL) or high speed
(USB_SPEED_HIGH). The udi_power field shows the power consump-
tion in milli-amps drawn at 5 volts, or zero if the device is
self powered.
If the device is a hub, the udi_nports field is non-zero, and the
udi_ports field contains the addresses of the connected devices.
If no device is connected to a port, one of the USB_PORT_* values
indicates its status.
USB_DEVICESTATS structusb_device_stats
This command retrieves statistics about the controller.
struct usb_device_stats {
u_long uds_requests[4];
};
The udi_requests field is indexed by the transfer kind, i.e.
UE_*, and indicates how many transfers of each kind that has been
completed by the controller.
USB_REQUEST structusb_ctl_request
This command can be used to execute arbitrary requests on the
control pipe. This is DANGEROUS and should be used with great
care since it can destroy the bus integrity.
The include file <dev/usb/usb.h> contains definitions for the types used
by the various ioctl(2) calls. The naming convention of the fields for
the various USB descriptors exactly follows the naming in the USB speci-
fication. Byte sized fields can be accessed directly, but word (16 bit)
sized fields must be access by the UGETW(field) and USETW(field, value)
macros to handle byte order and alignment properly.
The include file <dev/usb/usbhid.h> similarly contains the definitions
for Human Interface Devices (HID).
USB EVENT INTERFACE
All USB events are reported via the /dev/usb device. This devices can be
opened for reading and each read(2) will yield an event record (if some-
thing has happened). The poll(2) system call can be used to determine if
an event record is available for reading.
The event record has the following definition:
struct usb_event {
int ue_type;
#define USB_EVENT_CTRLR_ATTACH 1
#define USB_EVENT_CTRLR_DETACH 2
#define USB_EVENT_DEVICE_ATTACH 3
#define USB_EVENT_DEVICE_DETACH 4
#define USB_EVENT_DRIVER_ATTACH 5
#define USB_EVENT_DRIVER_DETACH 6
struct timespec ue_time;
union {
struct {
int ue_bus;
} ue_ctrlr;
struct usb_device_info ue_device;
struct {
usb_event_cookie_t ue_cookie;
char ue_devname[16];
} ue_driver;
} u;
};
The ue_type field identifies the type of event that is described. The
possible events are attach/detach of a host controller, a device, or a
device driver. The union contains information pertinent to the different
types of events. Macros, USB_EVENT_IS_ATTACH(ue_type) and
USB_EVENT_IS_DETACH(ue_type) can be used to determine if an event was an
``attach'' or a ``detach'' request.
The ue_bus contains the number of the USB bus for host controller events.
The ue_device record contains information about the device in a device
event event.
The ue_cookie is an opaque value that uniquely determines which device a
device driver has been attached to (i.e., it equals the cookie value in
the device that the driver attached to).
The ue_devname contains the name of the device (driver) as seen in, e.g.,
kernel messages.
Note that there is a separation between device and device driver events.
A device event is generated when a physical USB device is attached or
detached. A single USB device may have zero, one, or many device drivers
associated with it.
SEE ALSO
The USB specifications can be found at:
http://www.usb.org/developers/docs/aue(4), cue(4), kue(4), ohci(4), pci(4), ucom(4), ugen(4), uhci(4),
uhid(4), ukbd(4), ulpt(4), umass(4), ums(4), uplcom(4), urio(4),
uscanner(4), uvscom(4), usbd(8), usbdevs(8)HISTORY
The usb driver first appeared in FreeBSD 3.0.
AUTHORS
The usb driver was written by Lennart Augustsson <augustss@carlstedt.se>
for the NetBSD project.
FreeBSD 10.1 February 21, 1999 FreeBSD 10.1